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Publisher: Bristol : IOP × Subject: High resolution ×

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    Nanoplasmonic electron acceleration in silver clusters studied by angular-resolved electron spectroscopy
    (Bristol : IOP, 2012) Passig, J.; Irsig, R.; Truong, N.X.; Fennel, T.; Tiggesbäumker, J.; Meiwes-Broer, K.H.
    The nanoplasmonic field enhancement effects in the energetic electron emission from few-nm-sized silver clusters exposed to intense femtosecond dual pulses are investigated by high-resolution double differential electron spectroscopy. For moderate laser intensities of 10 14Wcm -2, the delaydependent and angular-resolved electron spectra show laser-aligned emission of electrons up to keV kinetic energies, exceeding the ponderomotive potential by two orders of magnitude. The importance of the nanoplasmonic field enhancement due to resonant Mie-plasmon excitation observed for optimal pulse delays is investigated by a direct comparison with molecular dynamics results. The excellent agreement of the key signatures in the delay-dependent and angular-resolved spectra with simulation results allows for a quantitative analysis of the laser and plasmonic contributions to the acceleration process. The extracted field enhancement at resonance verifies the dominance of surfaceplasmon-assisted re-scattering.
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    Energy and symmetry of dd excitations in undoped layered cuprates measured By Cu L3 resonant inelastic x-ray scattering
    (Bristol : IOP, 2011) Moretti Sala, M.; Bisogni, V.; Aruta, C.; Balestrino, G.; Berger, H.; Brookes, N.B.; De Luca, G.M.; Di Castro, D.; Grioni, M.; Guarise, M.; Medaglia, P.G.; Miletto, Granozio, F.; Minola, M.; Perna, P.; Radovic, M.; Salluzzo, M.; Schmitt, T.; Zhou, K.J.; Braicovich, L.; Ghiringhelli, G.
    We measured the high-resolution Cu L3 edge resonant inelastic x-ray scattering (RIXS) of undoped cuprates La2CuO4, Sr2CuO2Cl2, CaCuO2 and NdBa 2Cu3O6. The dominant spectral features were assigned to dd excitations and we extensively studied their polarization and scattering geometry dependence. In a pure ionic picture, we calculated the theoretical cross sections for those excitations and used these to fit the experimental data with excellent agreement. By doing so, we were able to determine the energy and symmetry of Cu-3d states for the four systems with unprecedented accuracy and confidence. The values of the effective parameters could be obtained for the singleion crystal field model but not for a simple two-dimensional cluster model. The firm experimental assessment of dd excitation energies carries important consequences for the physics of high-Tc superconductors. On the one hand, we found that the minimum energy of orbital excitation is always ≥ 1.4 eV, i.e. well above the mid-infrared spectral range, which leaves to magnetic excitations (up to 300 meV) a major role in Cooper pairing in cuprates. On the other hand, it has become possible to study quantitatively the effective influence of dd excitations on the superconducting gap in cuprates.